Many proposals, covering a very broad range of conceptual designs, have been made in the past for obtaining power from ocean waves. A number of these proposals, representative of this broad range, have been described by Panicker in an article entitled "Review of the Technology for Wave Power Conversion, " which appeared in the April 1976 issue of the Marine Technology Society Journal (Vol. 10, No. 3, pp. 7-15). In that article, these proposed devices are classified into four main groups: propulsion schemes, buoy power supply devices, shore based power stations, and offshore power plants.
Except in the second group comprising power supplies for buoys and navigational aids, successful development to an advanced engineering stage has not yet been reached by any of these previously proposed devices. Recently, however, new proposals in the last group comprising offshore power plants, to which the present invention relates, have been increasing markedly both in numbers and in sophistication.
One such scheme for an offshore power plant, based on the pumping action of a free-heaving vertical pipe containing a water column that is alternately entrained and then partially replaced by means of a check valve, has been described by Isaacs, Castel, and Wick in Ocean Engineering, Vol. 3, pp. 175-187 (1976). This scheme, which has been developed at the Scripps Institution of Oceanography, and is intended for use primarily along undeveloped coastal regions and islands in the trade wind belts, aims at achieving a substantial wave energy densification at the site of wave energy conversion through accumulation in time, together with a broad band range of response over wave amplitude and frequency.
Another recently proposed offshore power plant, wherein the primary means for wave energy extraction would by a partially submerged, pump-driving, rocking device with a special contour in the prevailing direction of wave travel, has been described by Salter in U.S. Pat. No. 3,928,967. This device, which is presently in the model testing stage under sponsorship of the British wave energy program, and is intended for use in seas of above average significant wave height in large scale multiple combinations forming a closely ordered linear array parallel to the prevailing wave fronts, has been found under laboratory tests to be capable of achieving power conversion efficiencies greater than 50 percent over a 2:1 range of wave periods. In heavy seas, however, as noted by Katory in the May 1976 issue of The Naval Architect (vol. 3, pp. 91-92), there will be problems in absorbing all the energy of the waves by a single linear array of such devices.
One possible way of attempting to resolve these problems, as further suggested by Katory, and as also proposed many years ago by Brady in the rather different context of his U.S. Pat. No. 1,757,166 (see also U.S. Pat. No. 4,036,563 issued to Tornqvist), would be to subject each oncoming wave form to a rectangular 2-dimensional succession of such linear arrays of wave energy absorbers, at spaced intervals along the wave form, and to extract a portion of the wave's energy at each interval.
As will be explained below, however, the three principal features of the present invention are precisely suited to treating just such problems as these, and to doing so in a wholly novel and fundamentally different way. But since the novelty of these particular features of the present invention depends, in turn, upon the cooperative functioning of a fundamentally and wholly novel class of wave energy removing impellers responsive to subsurface water movement, reference must also be made here to the state of the prior art relating to such impellers.
Although a multitude of different versions of such impellers have been proposed in the past, practically all of those versions constitute only minor variants of one or the other of two early prototypes, disclosed, respectively, in U.S. Pat. No. 574,177 issued to Stahl and Gatewood in 1896, and in U.S. Pat. No. 793,497 issued to Ariztia in 1905. On the other hand, the improvements over these two early prototypes that will be explained below are wholly and fundamentally new, just as are the principal functions that are intended to be performed by the improved impellers described herein.